Automated method and apparatus for mixing mud for use in well operations

ABSTRACT

Method and apparatus for mixing mud for use in well operations, including independently operable high and low capacity systems for supplying mud solids to a mixing tank. A radioactive, density measuring control system is employed which controls the rate of solids supply, with the same calibration setting being maintained for high and low rates of addition of solids material to the mud. A pneumatic conveying system is employed to convey the solids through the system. Vane-type feeders and mud shrouds are employed to minimize the dust level during the mud mixing operation.

United States Patent Terry 0. Anderson;

Darryl W. Rogers, both of Duncan, Okla. 771,954

Oct. 30, 1968 July 6, 1971 lhlliburton Company Duncan, Okla.

Inventors Appl. No, Filed Patented Assignee AUTOMATED METHOD ANDAPPARATUS FOR MIXING MUD FOR USE IN WELL OPERATIONS 22 Claims, 1 1Drawing Figs.

US. Cl 259/154, 259/ l 65 Int. Cl 1328c 7/04 Field oiSearch 259/154,

[56] References Cited UNITED STATES PATENTS 3,170,677 2/1965 Phister259/154 3,256,181 6/1966 Zingg 259/154 3,300,193 1/1967 Badgett 259/1544/1968 Putman 259/154 Primary Examiner-Robert W. Jenkins Attorney-Burns,Doane, Benedict, Swecker & Mathis ABSTRACT: Method and apparatus formixing mud for use in well operations, including independently operablehigh and low capacity systems for supplying mud solids to a mixing tank.A radioactive, density measuring control system is employed whichcontrols the rate of solids supply, with the same calibration settingbeing maintained for high and low'rates of addition of solids materialto the mud. A pneumatic conveying system is employed to convey thesolids through the system. Vane-type feeders and mud shrouds areemployed to minimize the dust level during the mud mixing operation.

PATENTED JUL 6 l9?! SHEFT 1 OF 4 i 's 1 .z g i I "4 a a z E g INVENTORSTERRY 0. ANDERSON DARRYL W. ROGERS J N ATTORNEYS BY 7 QMJ ZMMWPATENTEUJuL 6 l9?! SHEET 2 0F 4 FIG. 2

FIG. 4

FIG. 3

INVENTORS TERRY 0. ANDERSON DARRYL W ROGERS PATENTEUJUL 6 1911 SHEET 3OF 4 fil e H M M H Q "C 4 [LR .W E Q MS T N El L A L R R S N0 7 WM 0R RLT- )LF. 8 u an 4 9 L 3 k A Ml V HIGH LEVEL TRANSMITTER FIG .8

INVENTORS TERRY 0. ANDERSW DARRYL W. ROGERS PATENTED JUL. 6|97l v 5 147I saw u or 4 1 .0 INVENTORS TERRY 0. ANDERSON DARRYL W. ROGERS AUTOMATEDMETHOD AND APPARATUS FOR MIXING MUDFOR USE IN WELL OPERATIONS Modernwell-drilling operations are complex and costly operations.

A necessary facet of most drilling operations relates to the circulationof drilling mud through a well bore.

The function of the drilling mud is to remove cuttings, lubricate thedrilling bit, and provide a fluid of sufficient density in the boreholeto prevent fonnation fluids from blowing out or erupting out of the wellbore.

During drilling operations, the solids content of drilling mud may bereduced as a result of the solids caking out on the well bore. Inaddition, formation fluids may comingle with the mud so as to reduce thepercentage of the solids content. Regardless of how the solids contentof the drilled mud is reduced, the result of a reduction of solidscontent can be disastrous.

If an operator should be unaware that the density of the drilling mud isdecreasing as a result of a reduction in the percentage of solidscontent, he may well experience a blowout because the density of the mudis insufiicient to prevent well fluids from errupting out of the wellbore. Further, the density of the drilling mud may become so low as tobecome incapable of effectively removing cuttings, so as to impede theoverall drilling operation and create the danger of the drill stringbecoming stuck in the borehole.

A variety of systems have been employed for monitoring the density ofdrilling mud during a drilling operation. By and large thesedensity-monitoring systems have entailed densitometers providing avisual indication of mud density. As an operator observes variations indensity, by noting the density reading on a dial or chart, he endeavorsto insure that additional mud solids are added as required.

However, should an operator forget to monitor the densitometer readout,he may fail to observe that the solids content of the mud has becomedangerously low.

During normal drilling operations, the relative reduction in solidscontent of drilling mud will occur at a fairly low and constant rate.Thus, an operator may employ a low-volume handling system for addingsolids content to the mud to maintain an optimum solids content level.This low-volume addition of solids to the mud enables the solids to betransferred into a mixing tank with a fairly high degree of precision,so as to avoid wasting the relatively expensive solid constituents ofthe mud such as barite.

However, in the event of an emergency, such as when a well boreintersects a gas pocket or a fluid-bearing formation, gas or liquid froma formation may mingle with the mud at such a rapid rate as to require avastly accelerated addition of solids to the mud in order to prevent ablowout."

A system for handling such an accelerated addition of solids material todrilling mud will, of necessity, lack the precision involved in normalsystems for replenishing solids. Thus, for overall effectiveness andoptimized efficiency, it would be desirable to provide a mud-mixingsystem having the capability of adding solids at a relatively low rate,with precision accuracy in blending being maintained, and having analternative capacity to supply solids at an extremely high rate.

Oil field practice has developed to a point where radioactive-typedensitometers are being used with increasing frequency. However, suchdensitometers, in the past, have often required recalibration wherethere were significant variations in the level of barite material in thedrilling mud. For example, as is acknowledged in an article: RadioactiveMeasurement of Fluid Density," authored by D. G. Hartweg, forpresentation at the Petroleum Mechanical Engineering Conference in NewOrleans, Louisiana (U.S.) during Sept. of l960, it is noted that as muchas a 15 percent error may be introduced into density readings as aresult of changes in barite concentration, which changes areunaccompanied by recalibration of radioactive densitometers.

Thus, in the past, the nature of radioactive densitometers employed inoil field practices has been such as to introduce the possibility ofsubstantial error in a mud supply system which would fluctuate from alow to a high barite concentration.

It should also be recognized that during mud-mixing operations, it ishighly desirable to handle pulverulent solids, such as additives andbarite, in such a manner as to maintain controllable and regulated flow,consistent with the generation of minimum dust.

Thus, it is a principal object of the present invention to provide anautomated mud-mixing system for use in well operations and having acapacity to alternate between low and high rates of additions of solidmaterials to drilling mud.

It is likewise an object of the invention to provide such a mud-handlingsystem utilizing a radioactive densitometer which is capable ofproviding accurate density measurements, without requiringrecalibration, for both high and low rates of addition of solidsmaterial to the drilling mud.

Yet another principal object of the invention is to provide such animproved mud-handling system where, during normal or low-rate additionsof solids material to drilling mud, optimum accuracy in the addition ofsolids is maintained so as to avoid wasting solids material.

Another object of the invention is to provide such an improvedmud-mixing system uniquely incorporating a pneumatic system forconveying solids, operable with potentially independent but interactinghighand low-capacity systems, with the generation of dust beingminimized during both high and low rates of solids addition to the mud.

ln accomplishing at least some of the foregoing objects, there ispresented through this invention an apparatus for mixing material,which-apparatus includes mixing reservoir means and first dischargeconduit means extending from the mixing reservoir means. Adensity-measuring means is operable to measure the density of materialflowing through the first discharge conduit means. Return conduit means,included in the first discharge conduit means, is operable to return aportion of material from the first discharge conduit means to the mixingreservoir means.

The apparatus includes material supply means associated with seconddischarge conduit means. The second discharge conduit means is operableto discharge material from the supply means.

Also included in the apparatus is a first, relatively lowcapacity mixingmeans for supplying material to the mixing reservoir means. This firstmixing means includes a transfer reservoir means. A first branch conduitmeans is provided for conveying material from the second dischargeconduit means of the supply means into the transfer reservoir means. Afirst means, operable in response to the density-measuring means, servesto control a flow of material through the second branch conduit means enroute to the mixing means.

The apparatus further includes selectively operable actuating means foractuating the first and second mixing means.

Another individually significant aspect of this invention pertains to acombination including reservoir means and first supply means forsupplying a high-density material, at a relatively low rate, to thereservoir means. A second supply means is provided for supplyinghigh-density material to the reservoir means at a relatively high rate.A density-measuring means incorporated in the combination is operable tomeasure the density of material mixed in the reservoir means. Thisdensitymeasuring means includes radioactive, density-measuring meansoperable, substantially independent of the composition of mixedmaterial, to indicate mixed material density. The calibration of theradioactive density-measuring means is substantially the same when eachof the first and second supply means is independently supplying materialto the reservoir means.

Another significant facet of the invention entails a method for mixingmaterial where relatively dense material is supplied at a relatively lowrate to a reservoir. Relatively high-density material is subsequentlysupplied to the reservoir at a relatively high rate. The density of themixed material in the reservoir is measured by radioactivedensity-measuring means such that the calibration of the radioactivedensity-measuring means may remain the same, regardless of whethermaterial is being supplied to the reservoir at a high or low rate.

Other independently significant facets of the invention entail, in thecontext of the overall invention, unique method and apparatus aspects ofthe density-measuring system, involving a novel combination of photonenergy levels, means for blocking and attenuating of photons as theypass through material, and means for maintaining a relatively lowdiscrimination level in scintillation counting means upon which thephotons are impinged.

Other aspects worthy of note pertain to novel features of the first andsecond supply means, each incorporating a pneumatically impelled solidsmaterial source, a system for adding material independent of the firstand second supply means; and structural details of a control valve andsolid material storage units.

DRAWINGS In describing the invention, reference will be made topreferred embodiments illustrated in the appended drawings.

In the drawings:

FIG. 1 provides, in a schematic or diagrammatic format, an illustrationof the overall mud-mixing system of the present invention;

FIG. 2 provides an enlarged, partially sectioned vertical elevationalview of a control valve incorporated in the FIG. I assembly and utilizedto regulate the flow of air and pulverulent solids between supply tanksand a transfer reservoir of the FIG. 1 system;

FIG. 3 provides an enlarged, vertically sectioned, elevational view of avane-type pulverulent material discharge unit associated with each ofthe transfer and additive material reservoirs of the FIG. 1 system;

FIG. 4 provides an enlarged, vertically sectioned, elevational view of apulverulent material impelling system associated with each of thetransfer and additive material reservoirs of the FIG. 1 system;

FIG. 5 provides an enlarged, partially sectioned, elevational view of aradioactive densitometer incorporated in the FIG. 1 system and employedto monitor the density of mud mixed in a mixing reservoir anddischarging therefrom;

FIG. 6 provides a still further enlarged, transverse, horizontal andcross sectional view of the densitometer shown in FIG. 5 as viewed alongthe section line 6-6;

FIG. 7 provides an enlarged, vertically sectioned, elevational view ofan eductor-type discharge unit incorporated in the FIG. 1 system andutilized to provide a shroud of mud encircling a flow of air andpulverulent material being discharged into the mixing reservoir of theFIG. 1 system;

FIG. 8 provides, in schematic format, an illustration of a controlnetwork incorporated in the FIG. 1 system;

FIG. 9 provides a schematic or graphical representation of thecomponents of the FIG. 1 system which are employed to effect arelatively low rate of addition of solids material to drilling mud;

FIG. 10 provides a schematic or graphical representation of thecomponents of the FIG. 1 system which are employed to supply solids todrilling mud at a relatively high rate; and

FIG. 1 1 provides a schematic or graphical representation of thecomponents of the FIG. 1 system which are employed to supply additivematerial to drilling mud, independent of the material-adding componentsshown in FIGS. 9 and I0.

PRINCIPAL COMPONENTS OF SYSTEM FIG. I illustrates, in a schematicformat, the principal components of the mud mixing system I of thepresent invention.

System 1 includes a tanklike, mud-mixing reservoir 2. This tank 2 has anopen, material-receiving, upper end 2a.

A first discharge conduit 3 extends from the underside of the mixingreservoir or mud tank 2. Discharge conduit 3 conveys mud from the mixingtank 2 to a conventional mud pump 4. Mud discharged from the pump 4 isintended to be conveyed through conduit portions 3a, 3b and 3c of thedischarge conduit means 3 to a well site, not shown.

Flow of the mud to the well site may be controlled by a conventionalvalve 5, incorporated as shown in conduit section 3c.

A radioactive densitometer 6 is mounted, in series, in a conduit portion3d of the discharge conduit network. A portion of the mud dischargingthrough the conduit means 3 will flow through the densitometer 6 andconduit means 3d, and ultimately return to the upper end 211 of the mudtank 2 by way of a return conduit network 7.

System 1 additionally includes an assembly of pneumatically pressurized,pulverulent material reservoirs, defining solid material supply means 8.

Solid materials are conveyed from the supply means 8 to the upper end 20of the mixing tank 2 in order to maintain an acceptably high solidscontent in the mud being mixed. 7

During normal operations, solids materials are transferred from thesupply source 8 to the tank 2 by way of a first, relativelylow-capacity, mixing means 9.

During emergency conditions, when it may become necessary to drasticallyand rapidly increase the solids contents of the mud in the mixing tank2, pulverulent material is transferred from the supply means 8 to thetank 2 through a second, relatively high-capacity, solids transfer ordensitometer means 10.

Solids material from the supply source 8 is channeled alternatelythrough the low-capacity mixing means 9 or the high-capacity mixingmeans 10 under the influence of a manually operated control at thecontrol station 1 1.

At various points in time during the mud mixing operation, it may bedesirable to add certain additives to mud in the mixing tank 2. Forexample, it may be appropriate to add viscosity-modifying materials,loss circulation additives, etc. Such additives are transmitted to theopen upper end 2a of the mud tank 2 by way of an additive supplyingmeans 12. The operation of additive supplying means 12, under theinfluence of a manually adjustable control component 13, is entirelyindependent of the operation of the low-capacity mixing means 9 and thehigh-capacity mixing means 10. Thus, the system as a whole providesalternatively and selectively operable highand low-capacity mixingsystems for transferring the principal solids component of mud, such asbarite, from a supply reservoir system 8 to the mud tank. Augmentingcomponents 9 and 10, is the additive supply system 12.

The resultant density of mud being discharged from the reservoir 2 ismonitored by the radioactive densitometer 6, continuously throughout themud-mixing operation, and regardless of which of the units 9,10 or 12 isin operation.

In a manner to be hereinafter described, the density-monitoring unit 6provides automatic regulation of each of the lowcapacity andhigh-capacity units 9 and 10, depending upon which unit is in operationat a particular point in time.

The mud and density controlled mud is conveyed to the well site throughthe section 30 of discharge conduit 3b.

SUPPLY SYSTEM Supply system 8 includes a plurality of pulverulentmaterial containing reservoirs l3 and 14. Reservoir 13 may containpulverulent, mud-weighting material such as powdered barite.

Reservoir 14 may contain other powdered mud components,

Each of reservoirs 1.3'arid'l4 has its interior portion'c onnected''with' a source of pressurized air through an air-supplying, conduitnetwork 15. 'A branchconduit 1'6, controlled by'a valve l7, suppliespressurized air to the interior of reservoir 13. Another branch conduit18, controlled by a conventional valve 19, serves to supply pressurizedair to the interior of reservoir 14.

The air supplied tothe interior of the reservoirs l3 and 14 serves toaeratethe pulverulent material contained withinthese reservoirs andconvey the pulverulent material, in a generally fluidized form, out ofthe rescrvoirsl3 and 14, and through a second discharge conduit means20.

Discharge conduit means includes a branch portion 20a extending from.the discharge outlet 21 of reservoir; 13 to a main discharge section20b. Discharge conduit means 20 additionally includesa branch conduit20c, extending from the outlet of discharge mouth22 of reservoir 14 to.the main conduit portion 20b.

Manually operable valves 23 and 24 serve, respectively, to

control the flowof aerated pulverule'nt materials through the Duringthe. mud-mixing operation, while. low-capacity system'9 is in operation,thedensit'ometer 6 is continuously generated by densitometer 6, whichmay be digital in character, to a proportional control signal. Thiscontrol signal is transmitted through electricalconduit 3B'to anelectrical motor 39! Motor'39 is coupled to the hub or drive shaft 32 ofV the vane rotor 29.- 1

conduits 20a and 20c. By selectively manipulating the valves I 23 and24, a desired blending of pulverulent materials being discharged fromreservoirs '13 and 14 may be effected. This selectively blended solidsmaterial is. pneumatically conveyed toward the mixing eans 9' and 10,through the discharge conduit-20b. I I I I At this point, it may beappreciated that this material aerating' and conveying system may begenerally of the type described in the Bailey U.S. Pat. No. 3,226,422 orthe Hathorne U.S. Pat. No. 2,792,262, for example.

LOW-CAPACITY MIXING AND SUPPLY MEANS For an overall appreciation of themanner in which the relatively low-capacity system 9 is incorporated inthe overall operation, reference may be made to FIG. 1. However, tofacilitate the comprehension of the mode of operation of the low-levelsystem 9, reference may be made to FIG. 9 where the components of thelow-level system 9 are shown in isolated relation. System 9 may beconsidered as a first supply means, including supply means 8. I Thelow-capacity mixing means 9 includes an enclosed tank or reservoir 25. Afirst branch conduit 26 serves to convey blended solids material fromthe discharge conduit 20b .into the interior of the reservoir 25. Flowof pressurizedair and pulverulent material through branch conduit 26 iscontrolled by a selectively and manually (or automatically) operablevalve 27. I i

Pulverulent material is discharged from the lower end of the reservoirthrough a vane-typeoutlet 28. Outlet 28, as

shown in greater detail in FIG. 3, includes a vaned rotor 29 joumaled ina generally cylindrical housing 30. Rotor 29 defines a series ofmutually isolated, generally wedge-shaped pockets 31 circumferentiallyspaced about a rotor hub 32. The vane webs 33 of rotor 29, which definethe pockets 31, cooperate with housing m define a seal isolating thesolids material discharge mouth 34 from the interior portion 35 oftransfer reservoir 25. I I i As will thus be appreciated, the vane means28 provides an effective solids material metering, discharge device foreffecting precision control over the discharging of solids material fromthe transfer reservoir 25. In addition, the' vane means 28 provides aneffective dust seal, preventing dust generated by the introduction ofpressurized air and pulverulent material into the zone 35 fromcontaminating the external atmosphere ofthe tank 25.

As will beappreciated, it will be necessary to vent the interior space35 so as to prevent an excessive buildup of pneumatic pressure whichwould block the conveying of material through the discharge conduit 20.Thus, a vent line 36 communicating with the space 35, may be provided atan upper portion ofthe reservoir 25 Vent conduit 36 communicates withthe atmosphere and should be provided with an appropriate dust filter.

I or 35 of the reservoir 25.

Thus, the rotor 29 will rotate'at a rate dependent upon the density ofmud flowing through the conduit 3d, as-detected by the radioactivedensitometer 6. The conventional circuitry within control unit 11 willprovide an inversely proportional relationship between the radioactivelydetected mud density and the rate of vane or rotor rotation. That is tosay, as the detected mud density decreases, the rate of rotation of therotor 29 will increase'so as to tend to restore the muddensity to apredetermined value within a given time increment;

As will be appreciated, control unit 11 will include conventional,manually adjustable components for I presetting a desired mud density.Once the desired mud density is in-' troduced into the control network,components 28 and 6 will function as a servosystem, tending to maintainthis desired mud density,'comparing the densitometer generating signalwith the desired density signal level.

With the control over the feeding-of solids material to the mud tank-2being effected by the vane means 28, it is necessary, in relation to thesupply means 8, tomerely ensure that there is an adequate supply ofsolids material within the interi- This control may be effected bycontrol means, including a diaphragm or other type sensor 40incorporated within interior space 35 for determining a-desireduppermost level of solids material in the space 35. Another diaphragm orother type sensor is incorporated in a lower portion of space 35 and isintended to monitor an acceptable, lowermost level of solids materialwithin the-tank 25. Sensors and 4 l'gene'rate control signals and thesesignals are transmitted to control unit 11 through signal transmittingconduits 42 and 43, respectively.

The signals transmitted by conduits 42 and 43, are transmitted throughconventional circuitry within control unit 11 to an electrical, valveoff or valve on" signal. These electrical control signals arecommunicated through a signalt ransrnitting conduit 44 to a transducer45.-Transducer 45 comprises a conventional transducer for. convertingthe electrical control signal to a pneumatic control signal. Thispneumatic control signal regulates the pressure of air issuing from thetransducer 45 through an air conduit 46. la this case, it will beappreciated that pressurized air, modulated by the transducer, issupplied to unit 45 through a supply conduit 47.

The pneumatic control signal passing through the conduit 46 passes to aflow control valve 48 incorporated in the sec- Valves of this generaltype are described, for example, .in a

' Boteler U.S. Pat. No. 3,310,282 and a Boteler et al. U.S. Pat.

Valve 48, as shown in FIG. 2, comprises a body 49 defining an in-serie scontinuation of conduit section 20b. Valve-body I49 provide"s anupwardly facing weir 50 which projects trans:

versely across the interior of the second discharge conduit portion 20b;

A flexible diaphragm 51- is mounted in body 49 above the upper end 52 ofweir 50. This diaphragm 51 is operable to housing '56.. Operating rod 54is connected with a diaphragm 57. A coilfi spring 58 tends to'biasdiaphragm 57 and valve rod 54 downwardly so as to urgethe diaphragm 51,to a normally closed .or .faiI saIe valve position. A pneumatic signaltransmitted by transducer 45 through conduit 46 to a control signalgenerating chamber 59 acts on the'underside of diaphragm 57. When thecontrol signal indicates that the .valve is to be opened,,sufficie ntair pressure will be supplied .to the chamber 59 so as to move thediaphragm 57 upwardly and allow the diaphragm 51 to be raised so as toopen the passage 53.

In summary then, the valve on" or valve off" signals generated by thepulverulentmaterial level sensors 40 and 41 will determine the nature ofthe pneumatic signal transmitted to the valve 48 while the mixing means9 is in operation. This control system will ensure that the level ofpulverulent materi-.

al within the space 35 ismaintained within acceptablelimits.

Themetered flow of pulverulent solids discharging from vane means 28falls by gravity into the'open upper end 60 of a hopper61, shown inFIGS. '1 and 4. A f rst return branch conduitportion-7a of fretum'conduit means 7 returns mud from conduit means 3d to the tank 2 bycausing the mud to'pass through a jet-defining nozzle62. Jet definingnozzle 62 is coaxially' mounted atjone end of a discharge conduit" 63 ofhopper 61. Thus mud formed into a jet by nozzle 62 will comingle withsolids. material discharged by vane means 28 into hopper mouth 60. Thismud jet will impel the pulverulent solids through the hopper 611, withthe thus comingled mud and solids being discharged from conduit outlet64 into'the open upper end of the mud tank 2. i I l With thelow-capacity materials-mixing system having been described, it nowbecomes appropriate to consider the relatively high-capacity system 10.

HIGH-CAPACITY MIXING AND SUPPLY MEANS For anover'all appreciation of themanner in which the relatively high-capacity system is incorporated'inthe overall lated relation. System 10 may be considered as a second Isupplymeans, including supply unit 8.

High-capacity miitng means 10 includes a second branch conduit means 65which communicates .with the second discharge conduit means 20b.Asillustrated, second branch conduit 65 bypasses the transfer reservoir25. Flow through the branch conduit 65 is controlled by a manually (orautomatically) controlledvalve 66. a I 7 Branch conduit 65 conveyspressurized air and entrained solids to an eductor unit 67 (shown indetail in FIG. 7

' Eductor unit 67 includes a vertically extending inner conduit 68adapted to receive air and solids material at a T-junction at its upperend, from the branch conduit 65. In some instances, it may beappropriate to couple the terminus 36a of the vent conduit to the upperextremity of tube 68.

Tube 68 includes a lowermost outlet 69, disposed above the open mouth 2aof the mixing tank 2. Thus, pulverulent material conveyed to theinterior 70 of the tube 68 will be discharged by gravity from the outlet69 into the interior of mud tank 2.

A second return branch conduit 7b comprises a communicating portion ofthe return conduit network 7. At this point, it should be noted thatflow through the conduit means 7 is constrained so as to flow througheither the return branchconduit 70 or the branch conduit 7b dependingupon the manual or automatic setting of the conventional valves 71 and72 incorporated, respectively,in conduit sections 7a and 7b.

With valve 71 closed, and valve 72 open, mud will be returned from thedischarge conduit portion 3d through return branch conduit 7bto theeductor unit 68.

Eductor unit 68 includes annular shroud 73 which encircles the innertube 68 so as to define an annular mud-receiving cavity 74. Mudtransmitted through return branch conduit 7b signal will increase-Boasto permit a greater flow of solids to annular space 74 will provideannular mud stream, encircling the discharging air and pulverulentmaterial issuing from the discharge mouth 69. The mud encircled air'andpulverulent material will'discharge from the eductor unit 68 through theopenilower end 75 of shroud 73 and fall into the mixing tank 2.

Thus, duringthe high-capacity operation of the system 1, air-conveyedpulverulent material is conveyed from the supply means8 so as tocompletely bypass the transfer reservoir 25, and flow through thehigh-capacity eductor unit 68. The discharge of the high flow of solidsmaterial is enshrouded by mud so as to maintain effective dust control.

s During this high-level rate of solids material transfenthe rate ofmovement of solids is automatically controlled by the control valve 48.v

During the operation of the high-capacity system 10, the

densitometer 6 continuously monitors mud density, i.e., the

I through the signal-transmitting electrical conduit 37, is converted toa proportional electrical signal by conventional circuitry within thecontrol system 11. This proportional control signalqis converted to aproportional pneumatic control signal by transducer 45 and conveyed tothe control chamber 59 of the valve 48. e I I Here again it will beappreciated that the pneumatic control signal will be inverselyproportional to the mud density as detected by the densitometer 6. Thatis to say, as the detected density of the mud decreases, the intensityof the pneumatic material from the supply means 8 to the mixing tank 2by way of eductor unit 68. In this manner, the components 48 and 6 willfunction as a servosystem so as to tend tomaintain a desired highmuddensity. Control unit 6 contains. conventional signal comparison means,by-means of which the servosystcm will function to maintaina desireddensity level in the mud. The desired mud density setting may bemanually regulated inthe controlu'nit 11.

I ltwill be appreciated that where the valve 48 isspring biased to anopen'position, and pneumatically biased to a closed position, thepneumatic signal will be proportional to the densitometersignal. Inother words, the lower the detected density, in relation to a desireddensity, the lowcrwill be the air. pressure generated withinthe valvei48so as to, maintain the valveo pening at a size commensurate with therate of solids flow necessary to restore the desiredmud density within agiven time increment. I At this point, it should be noted that when thehigh-capacity system 10 is in operation, the valves 27 and 71 will beclosed, while the valves 66 and 72 will be open.

Conversely,fwhen the low-capacity unit 9 is in operation, the valves 27and 71 will be open, while the valves66 and 72 will be closed.

In some instances, where the vent tube 36 communicates with the eductor68, it may be desirable to permit some flow through the branch conduit7b, even when the low-capacity system 9 is in operation so asto providea mud shroudencircling the air being vented from the tank 25 through thevent 36. Thus, with this arrangement, a mud shroud would serve toprevent dissimination into the atmosphere of any residue dust that mightbe present in the air stream.

With the highand low-capacity systems 10 and 9, respectively, havingbeen described, it now becomes appropriate to consider structuraldetails of the additive supplying system 12.

ADDlTlVE-SUPPLYING SYSTEM For an' overall appreciation of the manner inwhich the addi-' tive supplying system .12 is incorporated inthe overalloperation, reference may be made to FIG. 1. However, to facilitate Theadditive supply system 12 as shown in FIG. 1, includes a hopper 76.Hopper 76 has an open upper end 77 into which bulk amounts of solidpulverulent additive material may be dumped. Hopper 76 may be providedwith a vane-type discharge unit 28' substantially identical to the vanemeans 28 associated with the transfer reservoir 25. The motor 39associated with the vane means 28 is coupled to the independent controlstation 13. Thus, by manipulating the controls of station 13, anoperator may cause the rotor of the vane means 28 to operate at adesired rate so as to discharge solids from the outlet 34 at any desiredrate.

Solids discharged from the outlet 34' of hopper 76 will fall by gravityinto a mixing unit 60' which may be considered to be functionallyidentical to the unit 60 associated with the transfer reservoir 25.

This unit 60' provides a conduit 63 for conveying additive material tothe open upper end 2a of the mud tank 2. Thus, additive material isdischarged by gravity from the outlet 64' of conduit 63' into the mudtank.

A third return branch conduit 78 is connected with discharge conduits 3band 3c and serves to convey a portion of the mud flowing to the wellheadback to ajet defining nozzle 62' of the unit 60. The flow of mud throughreturn conduit 78 is controlled by a manually operable valve 79.

Thus, mud conveyed to the nozzle 62' forms a mud jet operable to impeladditive material through the conduit 63' to the outlet 64.

It may be desired, in some instances, to add liquid-type additives tothe mud. To facilitate the addition of such additives, a fluid additivereservoir 80 may be provided. Reservoir 80 communicates with hopper 61of unit 60' by way of a conduit 81. The flow of liquid additive throughthe conduit 81 is controlled by a manually operable control valve 82.

At this point, the three major component supplying systems 9, l and 12have been described. It now becomes appropriate to consider specificdetails of the unique densitometer 6.

RADIOACTIVE DENSITOMETER The densitometer 6 comprises a novelradioactive densitometer of the type described in a pending U.S.application of Zimmerman et al., Ser. No. 729,291, filed May 15, 1968,now abandoned, entitled: Methods and Apparatus for Measuring SlurryDensity with Gamma Rays and assigned to the assignee of the presentapplication.

The densitometer 6, as shown in FIGS. 1, and 6, includes a tubular body83 incorporated, in series in, and defining a part of, conduit means 3d.

In the preferred embodiment, conduit means 3d and tubular body 83 extendvertically upwardly from pump discharge conduit 3a.

The densitometer 6 includes a generally horizontally extending body 84including clamplike segments 85 and 86, clamped about the periphery ofconduit section 83.

Housing portion 85 supports a detachable cartridge 87 including a photonemitter 88. In the preferred embodiment, the photon emitter 88 comprisesa Cs I37 source having an energy level of about 0.661 Mev. It iscontemplated that a photon emitter may be successfully employed wherethe energy level of the emitted photons is in the preferable energylevel range of about 0.6 to about 1.33 Mev. or acceptably between 0.6and 2 Mev.

Photons emitted from source 88 may pass through a generallyfrustoconical collimating passage 89. Collimating passage 89 is formedin a calibrating bar 90. In the manner described in the aforementionedZimmerman patent, a bar handle 91 may be pulled outwardly of abar-receiving recess 92, to move a calibrating portion 93 of bar 90 intoalignment with the emitter 88.

However, during normal operation, the bar 90 is in the retractedposition shown in FIG. 6, where the collimating passage 89 is coaxiallyaligned with the emission path of photons and diverges outwardly towardthe central passage 94 of the tubular member 83. The aligned axes ofemitter 88 and frustoconical collimating passage 89 perpendicularlyintersect the central vertical axis of the passage 94.

The tungsten carbide shielding mass 95 encircles the emitter 88 but doesnot occupy the axial path between the emitter 88 and the central passage94.

Body portion 86 supports an upright tubular component 96. Tubularcomponent 96 contains a removable, tubular housing 97. Housing 97supports, at its lower end, a scintillation counting means comprising athallium-activated, sodium iodide crystal 98. Superposed within a tube96 above the crystal 98, and optically coupled thereto by a silicon oilinterface 99 is a photomultiplier unit 100. Photomultiplier unit 100 maycomprise an EMI type 952S photomultiplier tube.

In the conventional fashion, photomultiplier tube 100 generates anelectric signal which may be digital in character, and is indicative ofthe absorption of photons by the mud flowing through the passage 94. Thesignal thus generated by the unit 100, which is indicative of muddensity, is transmitted through the aforementioned electrical conduit 37to the control unit 11.

Mounting tube 96 is supported in housing clamp portion 86 by a leadshielding mass 101. Lead shield 101 provides a lead barrier 102interposed between the passage 94 and the sodium iodide crystal 98. Thislead shield 102 should have a thickness D on the order of between about1 and 1.5 centimeters. This leadshield is then operable to substantiallyblock the passage of photons issuing from the mud in passage 94 whichhave a photon energy level of less than about 0.3 Mev. This lead shield102 additionally attenuates the passage of photons issuing from the mudin passage 94, which photons have a photon energy level of less thanabout 0.45 Mev., by at least twice the degree of attenuation of photonsissuing from passage 94 which have an energy level of about 0.6 Mev. orgreater.

As described in the Zimmerman application, the photomultiplier tube isoperated with an applied anode voltage operable to maintain a lowerdiscrimination level of about 0.05 Mev.

The overall consequence of these structural and functionalcharacteristics of the radioactive densitometer provides a densitometerwhich will accurately measure mud density over widely varying barite oradditive content with an accuracy deviating from actual density whichdoes not exceed about 0.3 pounds per gallon. This accuracy, of course,represents a substantial advance over the errors normally encounteredwhere calibration is not adjusted in accordance with varying baritepercentages, as discussed in the aforementioned Hartweg article.

OVERALL MODE OF OPERATION During normal operations of the system 1, therelatively low-capacity mixing unit 9 will be in operation. The mannerin which system 9 is operated, to the exclusion of system 10, may beappreciated by reference to the schematic illustration of controlnetwork 11 appearing in FIG. 8.

As shown in FIG. 8, the density signal is conveyed from the densitometer6 along electrical conduit 37 to a proportional signal generator ortransmitter 110. The proportional control signal may be conveyed fromunit 11a, in parallel along transmission paths 11b and lie. Transmissionpath 11b passes through a transmission control unit 11d whichelectrically communicates with electrical signal transmitting conduit44b.

Transmission means 11c communicates with another signaltransmittingcontrol unit lie. The signal transmitted along transmission path 11cexits from transmission control unit 1 1e so as to pass throughelectrical conduit 38 to the motor 39.

Transmitter 11d is provided with means for generating a control signalalong path 44b which constitutes a comparison between the measureddensity signal and a signal indicative of a desired, predetermined andselectively variable mud density. Thus, the signal generated along path44b will be a correction signal tending to induce the restoration of muddensity to a desired preset level. The signal in unit 11d, representingdesired mud density to be compared with actual measured density, may bemanually adjusted, in relation to the independent operation ofhigh-capacity unit 20.

Similarly, transmitter He may include an independently adjustablecomponent for effecting a comparison between the signal representingmeasured mud density and a signal representing a predetermined densityto be maintained while the unit 9 is in operation. As will beunderstood, the mud density to be maintained while unit 9 is inoperation will generally be less than that to be maintained while unitis in operation. Comparison between measured mud density and desired muddensity in unit lle, through conventional circuitry, will yield a muddensity correcting signal to be transmitted along the route 38 to themotor 39.

The high and low material level signals transmitted by conduits 42 and43 enter a material level, signal generator llf. The resulting controlsignal, produced by conventional circuitry within unit 11f, i.e. eithera valve on" or valve off signal, is transmitted through transmissioncontrol station lle into the transmission path 44a.

As shown in FIG. 8, transmission paths 44a and 44b both communicate withthe transmission path 44 leading to the valve-controlling transducer 45.Obviously, however, only one of these paths will be in operation at anyparticular time.

Manually operable switch means 11g, incorporated in the control station11, determines which of the transmission control means lld and lie is tobe operable, to the exclusion of the other.

Thus, when low-level mixing unit 9 is operable, switch 1 lg is operatedso as to cause unit 11d to block signal transmissions and permit unitlle to transmit control signals.

With unit 112 operable, the transducer 45 functions, in response to thelevel detectors 40 and 41 to maintain an adequate material level in thereservoir 25. The signal transmitted to the motor 39 provides a flow ofsolids material to the tank 2, in accordance with the mud densitymeasurement effected by the radioactive densitometer 6. As above noted,when unit 9 is in operation, valves 27 and 71 are open and valves 72 and66 are closed.

When high-capacity unit 10 is to be activated, valves 71 and 27 areclosed, while valves 72 and 66 are open. During this mode of operation,switch llg is activated so as to cause the unit lle to blocktransmission with the unit 11d permitting signal transmissions.

Thus, the density-correcting signal is transmitted to the transducer 45and controls the flow of pulverulent material through the valve 48 inaccordance with the density signal obtained from densitometer 6.

At any time during the operation of the system, the controller l3 of theadditive supply system 12 may be activated so as to introduce selectiveamounts of additives into the mud mixing hopper 2. in this connection,it will be appreciated that the amounts of additives supplied by thecomponent 12 will be limited so as to have little or no appreciableeffect on the density of the overall mud system. Thus, the additive unit12 will not significantly adversely afiect the operation of thedensitometer 6.

MAJOR ADVANTAGES AND SCOPE OF lNVENTlON A major advantage of theinvention resides in the provision of a mud-mixing system havingselectively operable, and independently novel highand lowcapacity,combination aspects. Augmenting these components for supplying theprincipal weighting constituents of the mud is an independently operableadditive supply system.

Thus, weighting material may be added to the mud at a relatively lowrate with precision blending accuracy being maintained. Where emergencyconditions arise, the system may be immediately converted to supplylarge quantities of weighting materials.

In this connection, it is contemplated that the low-capacity unit 9 willbe able to discharge solids at a rate of between 0.15 and 3.0 cubic feetper minute. The high-capacity system 10 should have a capacity of atleast several times this flow rate.

Regardless of whether weighting materials are being added at a low orhigh rate, maximum flexibility is maintained in that an operator maysupply additives, such as thickeners or loss circulation materials,without altering the operation of the mam mixing components.

The incorporation of the novel densitometer, in the context of theoverall system,.affords a particularly efiicient automated mud-mixingsystem where high-density material such as barite may be added atvarying rates without requiring recalibration of the densitometer andwhile maintaining high accuracy in density measurements.

The use of pneumatic conveying systems for transmitting pulverulentmaterial provides an enclosed high-capacity mixing system, and minimizesthe generation of dust. Dust generation is further controlled byutilizing vane-type feeders and mud shrouds.

The system i has been described from the standpoint of providing amud-mixing arrangement operable to maintain a preselected mud densitywhile the low-capacity unit 9 is in operation, and maintain anindependently preselected and adjustable density when the high-capacityunit 10 is in operation.

In certain instances, the control signal generated by the radioactivedensitometer 6 may be transmitted to a proportioner control mechanism tovary the ratio between solids and liquids in the reservoir 2. Where thismodification of the system is utilized, the control signal generated bydensitometer 6 would be transmitted to a conventional ratio controllercontaining a feed control mechanism for providing the desired additionof liquid to the reservoir 2.

In describing the invention, reference has been made to preferredembodiments. However, those skilled in the well art and familiar withthe disclosures of this invention may well envision additions,deletions, substitutions or other modifications which would fall withinthe purview of the invention as defined in the appended claims.

We claim:

1. An apparatus for mixing material, said apparatus comprising:

reservoir means;

first supply means, including a transfer reservoir means, for

conveying a high-density material, at a relative low rate, toward saidreservoir means;

second solids transfer supply means for conveying a highdensity materialtoward said reservoir means at a relative high rate; means forpneumatically conveying said high-density material to said first andsecond supply means whereby said pneumatic means provides an enclosedsystem thereby preventing hazardous dust conditions; and

density measuring means operable to measure the density of materialmixed in said reservoir means, said density measuring means, including acombination of photon energy levels and further including a radioactivedensity-measuring means operable, substantially independent of theamount of said high-density material in said mixed material, to indicatemixed material density, with the calibration of said radioactivedensity-measuring means being substantially the same when each of saidfirst and second supply means is independently supply material to saidreservoir means.

2. An apparatus for mixing mud to be used in well-drilling operations,said apparatus comprising:

mud-mixing, reservoir means;

first supply means, including a transfer reservoir means, for

supplying a high-density, pulverulent material, at a relative low rate,to said mud-mixing reservoir means;

second solids transfer supply means for supplying a highdensitypulverulent material to said mud-mixing reservoir means at a relativelyhigh rate;

density-measuring means operable to measure the density of mud mixed insaid mud-mixing reservoir means, said densitymeasuring means including acombination of photon energy levels and further including a radioactivedensity-measuring means operable, substantially independent of thecomposition of said mud, to indicate mud density, with the calibrationof said radioactive density-measuring means being substantially the samewhen each of saidfirst and second supply means is independentlysupplying pulverulent material to said mud-mixing reservoir means; meansresponsive to said density-measuring means for alternately regulatingthe flow of pulverulent material through said first and secondsupplymeans; and pneumatic conveying means for impelling pulverulent materialthrough each of said first and second supply means whereby saidpneumatic conveying means, providing an enclosed high-capacity mixingsystem, minimizes the generation of dust. 3. An apparatus for mixing mudto be used in well-drilling operations, said apparatus comprising:

mud-mixing, reservoir means; first supply means for'supplying apulverulent barite-containing material, at a relatively low rate, tosaid mixing reservoir means; second supply means for supplying apulverulent barite-containing material to said mixing reservoir means ata relatively' high rate; density-measuring means operable to measure thedensity of mud in said mixing reservoir means, said density-measuringmeans including radioactive density-measuring means operable,substantially independent of the composition ,of said mud, to indicatemuddensity, with the calibration of said radioactive density-measuringmeans being substantially the same when each of said first and secondsupply means is independently supplying pulverulent material to saidmixing reservoir means; said density-measuring means including a sourceof photons having a photon energy of between about 0.6 and about 2 Mev.positioned adjacent a vertical flow of said mud, means for collimatingthe emission of photons from said source en route to said mud, shieldingmeans for substantially blocking the passage of photons issuing fromsaid mud which have a photon energy level of less than about 0.3 Mev.and attenuating the passage of photons issuing from said mud having aphoton energy level of less than about 0.45 Mev. by at least twice thedegree of attenuation of photons issuing from said mud which have aphoton energy level v of about 0.6 Mev. or greater, scintillationcounting means, means for impinging photons which have been subjected tosaid blocking and attenuating on said scintillation counting means, andmeans maintaining a lower discrimination level of said scintillationcounting means at least as low as about 005 Mev.; means responsive tosaid density-measuring means for alternately regulating the -flow ofpulverulent material through said first and second supply means; andpneumatic conveying means for impelling pulverulent material througheach of said first and second supply means. 4. An apparatus for mixingmaterial, said apparatus comprising:

mixing reservoir means; first discharge conduit means extending fromsaid mixing reservoir means; v v density-measuring means operable tomeasure the density of material through said first discharge conduitmeans; return conduit means included in said first discharge conduitmeans and operable to return a portion of material from said firstdischargev conduit means to said mixing reservoir means; material supplymeans including 7 second, discharge conduit means operable to dischargematerial from said supply means;

first, relatively low-capacity, mixing means for supplying material tosaid mixing reservoir means, said firstmixing means including transferreservoir means, first branch conduit means for conveying material fromsaid second discharge conduit means of said supply means into saidtransfer reservoir means, first means responsive to saiddensity-measuring means for controlling the rate of discharge ofrmaterial from said transfer reservoir means into said mixing reservoirmeans, second, relatively high-capacity, mixing means for supply ingmaterial to said mixingireservoir means, said second mixing meansincluding second branch conduit means communicating 'with said seconddischarge conduit means of said supply means, said second branch conduitmeans bypassing said transfer reservoir means, second means, operable inresponse to said density-measuring means, to control a flow of air andmaterial through said second branch conduit means en route to saidmixing means; and selectively operable actuating means for actuatingsaid first and second mixing means. 5. An apparatus for mixing mud foruse in well-drilling operations, said apparatus comprising:

mixing reservoir means; first discharge conduit means extending fromsaid mixing reservoir means; 7 pump means operable to convey mud throughsaid first discharge conduit means; density-measuring means connectedwith said first discharge conduit means and operable to measure thedensity of mud flowing therethrough;

return conduit means included in said first discharge conduit means andoperable to return a portion of mud flow,

downstream of said density-measuring means, from said first dischargeconduit means to said mixing reservoir means; g

solid material supply means including air pressure containing, andenclosure-defining wal means operable to support -a mass of pulverulentmaterial,

means for supplying pressurized air to the interior of said enclosuredefining wall means, with said wall means being operable to maintainsuperam bient pressure within said wall means, and

second, discharge conduit means'operable to discharge pressurized airand pulverulent material from said supply means;

first, relatively low-capacity, mixing means for supplying pulverulentmaterial to said mixing reservoir means, said first mixing meansincluding transfer reservoir means,

first branch conduit means for conveying pressurized air and pulverulentmaterial from said second discharge conduit means of said solid materialsupply means into said transfer reservoir means,

first vane means defining a series of mutually isolated, rotatablepockets for discharging pulverulent material from said transferreservoir means to said mixing reservoir means,

said first vane means defining a seal between the interior of saidtransfer reservoir means and said mixing reservoir means,

first means responsive to said density-measuring means for controllingthe rate of discharge of pulverulent material from said transferreservoir means by said first vane means,

control means for controlling said conveying of pressurized air andpulverulent material through said first branch conduit means to saidtransfer reservoir means so as to regulate the amount of pulverulentmaterial in said transfer reservoir means,

first return branch conduit means communicating with said return conduitmeans, comingling means for comingling pulverulent material dischargedby said first vane means and mud passing through said first returnbranch conduit means, said comingling means including first jet-definingmeans operable to form mud flowing through said return conduit meansinto a jet stream operable to impel pulverulent material discharged bysaid first vane means; second, relatively high-capacity, mixing meansfor supplying pulverulent material to said mixing reservoir means, saidsecond mixing means including second branch conduit means communicatingwith said second discharge conduit means of said solid material supplymeans, said second branch conduit means bypassing said transferreservoir means, valve means, operable in response to saiddensity-measuring means, to control a flow of pressurized air andpulverulent material through said second branch conduit means, outletmeans for discharging pressurized air and pulverulent material from saidsecond branch conduit means toward said mixing reservoir means, secondreturn branch conduit means communicating with said return conduitmeans,

annular stream-defining means communicating with said.

second return branch conduit means and operable to define an annularflow of mud encircling pressurized air and pulverulent materialdischarging from said outlet means; I additive supplying means includingadditive material reservoir means, second vane means operable to definea series of mutually isolated rotatable pockets for dischargingsegregated quantities of additive material from said additive materialreservoir means, means for selectively controlling the rate of dischargeof additive material by said vane means, additive material conduit meansfor conveying additive material, discharged by said second vane means,to said mixing reservoir means, and third, return branch conduit meansconnected with said first discharge conduit means, and 7 secondjet-defining means operable to constrain mud flowing through said thirdreturn branch conduit means into a jet stream operable to impel additivematerial through said additive material conduit means; and selectivelyoperable actuating means for alternately actuating said first and secondmixing means, 6. An apparatus for mixing mud for use in well-drillingoperations, said apparatus comprising:

mixing reservoir means; first discharge conduit means extending fromsaid mixing reservoir means; pump means operable to convey mud throughsaid first discharge conduit means;

density-measuring means connected with said first discharge conduitmeans and operable to measure the density of mud flowing therethrough;said density-measuring means including a source of photons having aphoton energy of between about 0.6 and about 2 Mev. positioned adjacenta vertical flow of said mud, means for collimating the emission ofphotons from said source en route to said mud, shielding means forsubstantially blocking the passage of photons issuing from said mudwhich have a photon energy level of less than about 0.3 Mev. andattenuating the passage of photons issuing from said mud having a photonenergy level of less than about 0.45 Mev. by at least twice the degreeof attenuation of photons issuingfrom said mud'which have a photonenergy level v of about 0.6 Mev. or greater, scintillation countingmeans,

means for impinging phdtoris'which havebeen subjected to said blockingand attenuating'on' said scintillation counting means, and 1 Y meansmaintaining a lower discrimination level of said scintillation countingmeans at least as low asabout 0.05 Mev.; return conduit means includedin said first discharge conduit means and operable to return a portionof mud flow, downstream of said density-measuring means, from said firstdischarge conduit means to said mixing reservoir means; solid materialsupply means including air pressure containing, and enclosure-definingwall means operable to support a mass of pulverulent material, means forsupplying pressurized air to the interior of said enclosure-definingwall means, with said wall means being operable to maintain superambientpressure within said wall means, and second, discharge conduit meansoperable to discharge pressurized air and pulverulent material from saidsupply means; said solid material supply means further including a firstsource of pulverulent, barite-containing material, a second source ofpulverulent, additive material, and means for selectively blendingmaterials from said first and second sources for passage through saidsecond discharge conduitmeans; first, relatively low-capacity, mixingmeans for supplying pulverulent material to said mixing reservoir means,said first mixing means including transfer reservoir means, first branchconduit means for conveying pressurized air and pulverulent materialfrom said second discharge conduit means of said solid material supplymeans into said transfer reservoir means, first vane means defining aseries of mutually isolated rotatable pockets for dischargingpulverulent material from said transfer reservoir means to said mixingreservoir means, said first vane means defining a seal between theinterior of said transfer reservoir means and said mixing reservoirmeans, first means responsive to said density-measuring means forcontrolling the rate of discharge of pulverulent material from saidtransfer reservoir means by said first vane means, control means forcontrolling said conveying of pressurized 'air and pulverulent materialthrough said first branch conduit means to said transfer reservoir meansso as to regulate the amount of pulverulent material in said transferreservoir means, first return branch conduit means communicating withsaid return conduit means, comingling means for comingling pulverulentmaterial discharged by said first vane means and mud passing throughsaid first return branch conduit means,

said comingling means including first jet-defining meansv operable toform mud flowing through said return conduit means into a jet streamoperable to impel pulverulent material discharged by said first vanemeans; second relatively high-capacity, mixing means for supplyingpulverulent material to said mixing reservoir means, said second mixingmeans including second branch conduit means communicating with saidsecond discharge conduit means of said solid material supply means, saidsecond branch conduit means bypassing said transfer reservoir means,

valve means, operable in response to said density-measuring means, tocontrol aflow of pressurized air and pulverulent material through saidsecond branch conduit means,

said valve means including weir means extending partially transverselyacross said second discharge conduit means, diaphragm means operable tomove transversely through the interior of said second discharge conduitmeans, generally toward and away from said weir means, and diaphragmmoving means operable in response to said density-measuring means,outlet means for discharging pressurized air and pulverulent materialfrom said second branch conduit means toward said mixing reservoirmeans, second return branch conduit means communicating with said returnconduit means, annular stream-defining means communicating with saidsecond return branch conduit means and operable to define an annularflow of mud encircling pressurized air and pulverulent materialdischarging from said outlet means; additive-supplying means includingadditive material reservoir means, second vane means operable to definea series of mutually isolated rotatable pockets for dischargingsegregated quantities of additive material from said additive materialreservoir means, means for selectively controlling the rate of dischargeof additive material by said vane means, additive material conduit meansfor conveying additive material discharged by said second vane means tosaid mixing reservoir means, and third, return branch conduit meansconnected with said first discharge conduit means, and secondjet-defining means operable to constrain mud flowing through said thirdreturn branch conduit means into a jet stream operable to impel additivematerial through said additive material conduit means; and selectivelyoperable actuating means for alternately actuating said first and secondmixing means. 7. A method for mixing material, said method comprising:supplying a high-density material from first supply means, at

a relatively low rate, to reservoir means; supplying high-densitymaterial from second supply means to said reservoir means at arelatively high rate; measuring the density of mixed material in saidreservoir means, said measuring being effected with radioactivedensity-measuring means, having a source of photons with a photon energylevel of between about 0.6 and about 2 Mev.; regulating an alternateflow of material through said first and second supply means in responseto said measuring, while maintaining a substantially constantcalibration of said radioactive density-measuring means. 8. A method formixing mud to be used in well-drilling operations, said methodcomprising:

supplying a pulverulent barite-containing material from first supplymeans, at a relatively low rate, to mud-mixing reservoir means;supplying pulverulent, barite-containing material from second supplymeans to said mixing reservoir means at a relatively high rate;measuring the density of mud in said mixing reservoir means, saidmeasuring being effected by positioning a source of photons having aphoton energy of between about 0.6 and about 2 Mev. adjacent a verticalflow of said mud, substantially blocking the passage of photons issuingfrom said mud which have a photon energy level of less than about 0.3Mev., and attenuating the passage of photons issuing from said mudhaving a photon energy level of less than about 0.45 Mev. by at leasttwice the degree of attenuation of photons issuing from said mud whichhave a photon energy level of about 0.6 Mev. or greater, and

impinging photons which h ave been subjected to said blocking andattenuating on photon-counting means; 7 and alternately regulating theflow of pulverulent material through said first and second supply meansin response to said measuring. 9. A method for mixing mud to be used inwell-drilling operations, said method comprising:

supplying a pulverulent barite-containing material from first supplymeans, at a relatively low rate, to mud-mixing reservoir means;supplying pulverulent, barite-containing material from second supplymeans to said mixing reservoir means at a relatively high rate;measuring the density of mud in said mixing reservoir means, saidmeasuring being effective by positioning a source of photons having aphoton energy of between about 0.6 and about 2 Mev. adjacent a verticalflow of said mud, collimating the emission of photons from said sourceen route to said mud, substantially blocking the passage of photonsissuing from said mud which have a photon energy level of less thanabout 0.3 Mev., attenuating the passage of photons issuing from said mudhaving a photon energy level of less than about 0.45 Mev. by at leasttwice the degree of attenuation of photons issuing from said mud, whichhave a photon energy level of about 0.6 Mev. or greater, impingingphotons which have been subjected to said blocking and attenuating onscintillation counting means, and maintaining a lower discriminationlevel of said scintillation counting means at least as low as about 0.05Mev.; alternately regulating the flow of pulverulent material throughsaid first and second supply means in response to said measuring; andpneumatically impelling said material through each of said first andsecond supply means. 10. A method for mixing mud to be used in welldrilling operations, said method comprising:

supplying a pulverulent barite-containing material from first supplymeans, at a relatively low rate, to mud-mixing reservoir means;supplying pulverulent, barite-containing material from second supplymeans to said mixing reservoir means at a relatively high rate;measuring the density of mud in said mixing reservoir means, saidmeasuring means being effected by positioning a Cs 137 source of photonshaving a photon energy of about 0.66l Mev. adjacent a vertical flow ofsaid mud, collimating the emission of photons from said source en routeto said mud, substantially blocking the passage of photons issuing fromsaid mud which have a photon energy level of less than about 03 Mev.,attenuating the passage of photons issuing from said mud having a photonenergy level of less than about 0.45 Mev. by at least twice the degreeof attenuation of photons issuing from said mud, which have a photonenergy level of about 0.6 Mev. or greater, impinging photons which havebeen subjected to said blocking and attenuating on a thallium-activatedsodium iodide crystal, and maintaining a lower discrimination level ofsaid scintillation counting means at least as low as about 0.05 Mev.;regulating an alternate flow of pulverulent material through said firstand second supply means in response to said measuring; pneumaticallyimpelling said material through each of said first and second supplymeans;

adding additional mud additive substances to said mixing reservoir meansat a rate of addition independent of said measuring; and

impelling at least a portion of said barite material with a mud jet enroute to said reservoir means.

11. A method for mixing material, said method comprising:

supplying a high-density material from first supply means, at

a relatively low rate, to reservoir means;

supplying high-density material from second supply means to saidreservoir means at a relatively high rate;

impelling at least a portion of said high-density material with a mudjet en route to said reservoir means;

measuring the density of mixed material in said reservoir means, saidmeasuring being effected with density-measuring means;

regulating an alternate flow of material through said first and secondsupply means in response to said measuring, while maintaining asubstantially constant calibration of said density-measuring means.

12. A method for mixing material, said method comprising:

supplying a high-density material from first supply means, at arelatively low rate, to reservoir means;

supplying high-density material from second supply means to saidreservoir means at a relatively high rate;

pneumatically impelling said high-density material through each of saidfirst and second supply means;

measuring the density of mixed material in said reservoir means, saidmeasuring being effected with measuring means; and

regulating an alternate flow of material through said first and secondsupply means in response to said measuring, while maintaining asubstantially constant calibration of said measuring means.

13. An apparatus for mixing material, said apparatus comprising:

reservoir means;

first supply means for supplying a high-density material, at arelatively low rate, to said reservoir mezms;

second supply means for supplying a high-density material to saidreservoir means at a relatively high rate;

means for pneumatically conveying said high-density material througheach of said first and second supply means; and

density-measuring means operable to measure the density of materialmixed in said reservoir means, said densitymeasuring means beingoperable, substantially independent of the composition of said mixedmaterial, to indicate mixed material density, with the calibration ofsaid measuring means being substantially the same when each of saidfirst and second supply means is independently supplying material tosaid reservoir means.

14. An apparatus for mixing material, said apparatus comprising:

reservoir means;

first supply means for supplying a high-density material, at arelatively low rate, to said reservoir means, said first supply meansincluding a transfer reservoir means;

second supply means for supplying a high-density material to saidreservoir means at a relatively high rate; and

density-measuring means operable to measure the density of materialmixed in said reservoir means, said densitymeasuring means includingdensity-measuring means operable, substantially independent of thecomposition of said mixed material, to indicate mixed material density,with the calibration of said density-measuring means being substantiallythe same when each of said first and second supply means isindependently supplying material to said reservoir means.

15. An apparatus for mixing mud for use in well-drilling operations,said apparatus comprising:

mixing reservoir means;

first discharge conduit means extending from said mixing reservoirmeans;

pump means operable to convey mud through said first discharge conduitmeans; density-measuring means connected with said first dischargeconduit means and operable to measure the density of mud flowingtherethrough; return conduit means included in said first dischargeconduit means and operable to return a portion of mud flow, downstreamof said density-measuring means, from said first discharge conduit meansto said mixing reservoir means; solid material supply means includingair pressure containing, and enclosure-defining wall means operable tosupport a mass of pulverulent material, means for supplying pressurizedair to the interior of said enclosure-defining wall means, with saidwall means being operable to maintain superambient pressure within saidwall means, and second, discharge conduit means operable to dischargepressurized air and pulverulent material from said supply means; andmixing means for supplying pulverulent material to said mixing reservoirmeans, said mixing means including transfer reservoir means, branchconduit means for conveying pressurized air and pulverulent materialfrom said second discharge conduit means of said solid material supplymeans into said transfer reservoir means,

material-transferring seal means defining a seal between the interior ofsaid transfer reservoir means and said mixing reservoir means, butoperable to discharge pulverulent material to said mixing reservoirmeans, means responsive to said density-measuring means for controllingthe rate of discharge of pulverulent material from said transferreservoir means by said seal means, control means for controlling saidconveying of pressurized air and pulverulent material through saidbranch conduit means to said transfer reservoir means so as to regulatethe amount of pulverulent material in said transfer reservoir means,return branch conduit means communicating with said return conduitmeans, and comingling means for comingling pulverulent materialdischarged by said seal means and mud passing through said return branchconduit means, said comingling means including jet-defining meansoperable to form mud flowing through said return conduit means into ajet stream operable to'impel pulverulent material discharged by saidseal means. 16. An apparatus for mixing mud for use in well-drillingoperations, said apparatus comprising:

mixing reservoir means; first discharge conduit means extending fromsaid mixing reservoir means; pump means operable to convey mud throughsaid first discharge conduit means; density-measuring means connectedwith said first discharge conduit means and operable to measure thedensity of mud flowing therethrough; said density-measuring meansincluding a source of photons having a photon energy of between about0.6 and about 2 Mev. positioned adjacent a vertical flow of said mud,means for collimating the emission of photons from said source en routeto said mud, shielding means for substantially blocking the passage ofphotons issuing from said mud which have a photon energy level of lessthan abut 0.3 Mev. and attenuating the passage of photons issuing fromsaid mud having a photon energy level of less than about 0.45 Mev. by atleast twice the degree of attenuation of photons issuing from said mudwhich have a photon energy level of about 0.6 Mev. or greater,scintillation counting means,

means for impinging photons which have been subjected to said blockingand attenuating on said scintillation counting means, and meansmaintaining a lower discrimination level of said scintillation countingmeans at least as low as about 0.05 Mev.; return conduit means includedin said first discharge conduit means and operable to return a portionof mud flow, downstream of said density-measuring means, from said firstdischarge conduit means to said mixing reservoir means; solid materialsupply means including air pressure containing, and enclosure-definingwall means operable to support a mass of pulverulent material, means forsupplying pressurized air to the interior of said enclosure-definingwall means, with said wall means being operable to maintain superambientpressure within said wall means, and second, discharge conduit meansoperable to discharge pressurized air and pulverulent material from saidsupply means; said solid material supply means further including a firstsource of pulverulent, barite-containing material, a

second source of pulverulent, additive material, and means forselectively blending materials from said first and second sources forpassage through said second discharge conduit means; and mixing meansfor supplying pulverulent material to said mixing reservoir means, saidmixing means including transfer reservoir means, branch conduit meansfor conveying pressurized air and pulverulent material from said seconddischarge conduit means of said solid material supply means into saidtransfer reservoir means, vane means defining a series of mutuallyisolated rotatable pockets for discharging pulverulent material fromsaid transfer reservoir means to said mixing reservoir means, said vanemeans defining a seal between the interior of said transfer reservoirmeans and said mixing reservoir means, means responsive to saiddensity-measuring means for controlling the rate of discharge ofpulverulent material from said transfer reservoir means by said vanemeans, control means for controlling said conveying of pressurized airand pulverulent material through said branch conduit means to saidtransfer reservoir means so as to regulate the amount of pulverulentmaterial in said transfer reservoir means,

return branch conduit means communicating with said return conduitmeans, and comingling means for comingling pulverulent materialdischarged by said vane means and mud passing through Said return branchconduit means, said comingling means including jet-defining meansoperable to form mud flowing through said return conduit means into ajet stream operable to impel pulverulent material discharged by saidvane means. 17. An apparatus for mixing mud for use in well-drillingoperations, said apparatus comprising:

mixing reservoir means; first discharge conduit means extending fromsaid mixing reservoir means; pump means operable to convey mud throughsaid first discharge conduit means; density-measuring means connectedwith said first discharge conduit means and operable to measure thedensity of mud flowing therethrough; return conduit means included insaid first discharge conduit means and operable to return a portion ofmud flow, downstream of said density-measuring means, from said firstdischarge conduit means to said mixing reservoir means; solid materialsupply means including air pressure containing, and enclosure-definingwall means operable to support a mass of pulverulent material, means forsupplying pressurized air to the interior of said enclosure-definingwall means, with said wall means being operable to maintain superambientpressure within said wall means, and second, discharge conduit meansoperable to discharge pressurized air and pulverulent material from saidsupply means; and mixing means for supplying pulverulent material tosaid mixing reservoir means, said mixing means including branch conduitmeans communicating with said second discharge conduit means of saidsolid material supply means, said branch conduit means bypassing saidtransfer reservoir means, valve means, operable in response to saiddensity-measuring means, to control a flow of pressurized air andpulverulent material through said branch conduit means, outlet means fordischarging pressurized air and pulverulent material from said branchconduit means toward said mixing reservoir means, return branch conduitmeans communicating with said return conduit means, and annularstream-defining means communicating with said return branch conduitmeans and operable to define an annular flow of mud encirclingpressurized air and pulverulent material discharging from said outletmeans. I& An apparatus for mixing mud for use in well-drillingoperations, said apparatus comprising:

mixing reservoir means; first discharge conduit means extending fromsaid mixing reservoir means; pump means operable to convey mud throughsaid first discharge conduit means; density-measuring means connectedwith said first discharge conduit means and operable to measure thedensity of mud flowing therethrough; said density-measuring meansincluding a source of photons having a photon energy of between about0.6 and about 2 Mev. positioned adjacent a vertical flow of said mud,means for collimating the emission of photons from said source en routeto said mud, shielding means for substantially blocking the passage ofphotons issuing from said mud which have a photon energy level of lessthan about 0.3 Mev. and attenuating the passage of photons issuing fromsaid mud having a photon energy level of less than about 0.45 Mev. by atleast twice the degree of attenuation of photons issuing from said mudwhich have a photon energy level of about 0.6 Mev. or greater,scintillation counting means, means for impinging photons which havebeen subjected to said blocking and attenuating on said scintillationcounting means, and means maintaining a lower discrimination level ofsaid scintillation counting means at least as low as about 0.05 Mev.;return conduit means included in said first discharge conduit means andoperable to return a portion of mud flow, downstream of saiddensity-measuring means, from said first discharge conduit means to saidmixing reservoir means; solid material supply means including airpressure containing, and enclosure-defining wall means operable tosupport a mass of pulverulent material, means for supplying pressurizedair to the interior of said enclosure-defining wall means, with saidwall means being operable to maintain superambient pressure within saidwall means, and second, discharge conduit means operable to dischargepressurized air and pulverulent material from said supply means;

said solid material supply means further including a first source ofpulverulent, barite-containing material,

a second source of pulverulent, additive material, and means forselectively blending materials from said first and second sources forpassage through said second discharge conduit means; and

mixing means for supplying pulverulent material to said mixing reservoirmeans, said mixing means including branch conduit means communicatingwith said second discharge conduit means of said solid material supplymeans, said branch conduit means bypassing said transfer reservoirmeans, valve means, operable in response to said density-measuringmeans, to control a flow of pressurized air and pulverulent materialthrough said branch conduit mean said valve means including v weir meansextending partially transversely across said second discharge conduitmeans,

diaphragm means operable to move transversely through the interior ofsaid second discharge conduit means, generally toward and away from saidweir means, and

diaphragm moving means operable in response to said density-measuringmeans, outlet means for discharging pressurized air and pulverulentmaterial from said branch conduit means toward said mixing reservoirmeans, return branch conduit means communicating with said returnconduit means, and

annular stream-defining means communicating with said return branchconduit means and operable to define an annular flow of mud encirclingpressurized air and pulverulent material discharging from said outletmeans.

19. An apparatus for mixing material, said apparatus comprising:

reservoir means;

pneumatic means for conveying pneumatically impelled material towardsaid reservoir means;

means operable to flow with said pneumatically conveyed material towardsaid reservoir means;

means to comingle at least a portion of said material with a mud jet enroute to said reservoir means; and

density-measuring means operable to measure the density of materialmixed in said reservoir means, said densitymeasuring means includingradioactive density-measuring means operable, substantially independentof the composition of said mixed material, to indicate mixed materialdensity.

20. Apparatus for mixing material, said apparatus comprismeans forsupplying pulverulent material from supply means to mixing reservoirmeans; means for measuring the density of mixed material in said mixingreservoir means, said measuring means including means positioning asource of photons having a photon energy of between about 0.6 and 2 Mev.adjacent a flow of said mixed material, means substantiallyblocking thepassage of photons issuing from said mixed material which have a photonenergy level ofless than about 0.3 Mev., means attenuating the passageof photons issuing from said mixed material having a photon energy levelof less than about 0.45 Mev. by at least twice the degree of attenuationof photons issuing from said mixed material which have a photon energylevel of about 0.6 Mev. or greater, and means for impinging photonswhich have been subjected to said blocking and attenuating on photoncounting means; means regulating a flow of pulverulent material throughsaid supply means in response to said measuring; means pneumaticallyimpelling said pulverulent material through said supply means; and meansconveying at least a portion of said pulverulent material with liquid enroute to said reservoir means. 21. A method for mixing material, saidmethod comprising:

pneumatically impelling material toward reservoir means; conveying saidpneumatically impelled material with a liquid stream toward saidreservoir means; measuring the density of material mixed in saidreservoir means with density-measuring means including radioactivedensity-measuring means operable, substantially independent of thecomposition of said mixed material, to indicate mixed material density;and regulating the flow of said pneumatically impelled material inresponse to said measuring. 22. A method for mixing material, saidmethod comprising: supplying pulverulent material from supply means tomixing reservoir means; measuring the density of mixed material in saidmixing reservoir means, said measuring means being effected bypositioning a source of photons having a photon energy of between about0.6 and 2 Mev. adjacent a flow of said mixed material, substantiallyblocking the passage of photons issuing from said mixed material whichhave a photon energy level of less than about 03 Mev., attenuating thepassage of photons issuing from said mixed material having a photonenergy level of less than about 0.45 Mev. by at least twice the degreeof attenuation of photons issuing from said mixed material, which have aphoton energy level of about 0.6 Mev. or greater, and impinging photonswhich have been subjected to said blocking and attenuating on photoncounting means; regulating a flow of pulverulent material through saidsupply means in response to said measuring; pneumatically impelling saidpulverulent material through said supply means; and conveying at least aportion of said pulverulent material with a liquid en route to saidreservoir means.

1. An apparatus for mixing material, said apparatus comprising:reservoir means; first supply means, including a transfer reservoirmeans, for conveying a high-density material, at a relative low rate,toward said reservoir means; second solids transfer supply means forconveying a high-density material toward said reservoir means at arelative high rate; means for pneumatically conveying said high-densitymaterial to said first and second supply means whereby said pneumaticmeans provides an enclosed system thereby preventing hazardous dustconditions; and density measuring means operable to measure the densityof material mixed in said reservoir means, said density measuring means,including a combination of photon energy levels and further including aradioactive density-measuring means operable, substantially independentof the amount of said highdensity material in said mixed material, toindicate mixed material density, with the calibration of saidradioactive density-measuring means being substantially the same wheneach of said first and second supply means is independently supplymaterial to said reservoir means.
 2. An apparatus for mixing mud to beused in well-drilling operations, said apparatus comprising: mud-mixing,reservoir means; first supply means, including a transfer reservoirmeans, for supplying a high-density, pulverulent material, at a relativelow rate, to said mud-mixing reservoir means; second solids transfersupply means for supplying a high-density pulverulent material to saidmud-mixing reservoir means at a relatively high rate; density-measuringmeans operable to measure the density of mud mixed in said mud-mixingreservoir means, said density-measuring means including a combination ofphoton energy levels and further including a radioactivedensity-measuring means operable, substantially independent of thecomposition of said mud, to indicate mud density, with the calibrationof said radioactive density-measuring means being substantially the samewhen each of said first and second supply means is independentlysupplying pulverulent material to said mud-mixing reservoir means; meansresponsive to said density-measuring means for alternately regulatingthe flow of pulverulent material through said first and second supplymeans; and pneumatic conveying means for impelling pulverulent materialthrough each of said first and second supply means whereby saidpneumatic conveying means, providing an enclosed high-capacity mixingsystem, minimizes the generation of dust.
 3. An apparatus for mixing mudto be used in well-drilling operations, said apparatus comprising:mud-mixing, reservoir means; first supply means for supplying apulverulent barite-containing material, at a relatively low rate, tosaid mixing reservoir means; second supply means for supplying apulverulent barite-containing material to said mixing reservoir means ata relatively high rate; density-measuring means operable to measure thedensity of mud in said mixing reservoir means, said density-measuringmeans including radioactive density-measuring means operable,substantially independent of the composition of said mud, to indicatemud density, with the calibration of said radioactive density-measuringmeans being substantially the same when each of said first and secondsupply means is independently supplying pulverulent material to saidmixing reservoir means; said density-measuring means including a sourceOf photons having a photon energy of between about 0.6 and about 2 Mev.positioned adjacent a vertical flow of said mud, means for collimatingthe emission of photons from said source en route to said mud, shieldingmeans for substantially blocking the passage of photons issuing fromsaid mud which have a photon energy level of less than about 0.3 Mev.and attenuating the passage of photons issuing from said mud having aphoton energy level of less than about 0.45 Mev. by at least twice thedegree of attenuation of photons issuing from said mud which have aphoton energy level of about 0.6 Mev. or greater, scintillation countingmeans, means for impinging photons which have been subjected to saidblocking and attenuating on said scintillation counting means, and meansmaintaining a lower discrimination level of said scintillation countingmeans at least as low as about 0.05 Mev.; means responsive to saiddensity-measuring means for alternately regulating the flow ofpulverulent material through said first and second supply means; andpneumatic conveying means for impelling pulverulent material througheach of said first and second supply means.
 4. An apparatus for mixingmaterial, said apparatus comprising: mixing reservoir means; firstdischarge conduit means extending from said mixing reservoir means;density-measuring means operable to measure the density of materialthrough said first discharge conduit means; return conduit meansincluded in said first discharge conduit means and operable to return aportion of material from said first discharge conduit means to saidmixing reservoir means; material supply means including second,discharge conduit means operable to discharge material from said supplymeans; first, relatively low-capacity, mixing means for supplyingmaterial to said mixing reservoir means, said first mixing meansincluding transfer reservoir means, first branch conduit means forconveying material from said second discharge conduit means of saidsupply means into said transfer reservoir means, first means responsiveto said density-measuring means for controlling the rate of discharge ofmaterial from said transfer reservoir means into said mixing reservoirmeans, second, relatively high-capacity, mixing means for supplyingmaterial to said mixing reservoir means, said second mixing meansincluding second branch conduit means communicating with said seconddischarge conduit means of said supply means, said second branch conduitmeans bypassing said transfer reservoir means, second means, operable inresponse to said density-measuring means, to control a flow of air andmaterial through said second branch conduit means en route to saidmixing means; and selectively operable actuating means for actuatingsaid first and second mixing means.
 5. An apparatus for mixing mud foruse in well-drilling operations, said apparatus comprising: mixingreservoir means; first discharge conduit means extending from saidmixing reservoir means; pump means operable to convey mud through saidfirst discharge conduit means; density-measuring means connected withsaid first discharge conduit means and operable to measure the densityof mud flowing therethrough; return conduit means included in said firstdischarge conduit means and operable to return a portion of mud flow,downstream of said density-measuring means, from said first dischargeconduit means to said mixing reservoir means; solid material supplymeans including air pressure containing, and enclosure-defining wallmeans operable to support a mass of pulverulent material, means forsupplying pressurized air to the interior of said enclosure definingwall means, with said wall means being operable to maintain superambientpressure within said wall means, and second, discharge conduit meansoperable to disCharge pressurized air and pulverulent material from saidsupply means; first, relatively low-capacity, mixing means for supplyingpulverulent material to said mixing reservoir means, said first mixingmeans including transfer reservoir means, first branch conduit means forconveying pressurized air and pulverulent material from said seconddischarge conduit means of said solid material supply means into saidtransfer reservoir means, first vane means defining a series of mutuallyisolated, rotatable pockets for discharging pulverulent material fromsaid transfer reservoir means to said mixing reservoir means, said firstvane means defining a seal between the interior of said transferreservoir means and said mixing reservoir means, first means responsiveto said density-measuring means for controlling the rate of discharge ofpulverulent material from said transfer reservoir means by said firstvane means, control means for controlling said conveying of pressurizedair and pulverulent material through said first branch conduit means tosaid transfer reservoir means so as to regulate the amount ofpulverulent material in said transfer reservoir means, first returnbranch conduit means communicating with said return conduit means,comingling means for comingling pulverulent material discharged by saidfirst vane means and mud passing through said first return branchconduit means, said comingling means including first jet-defining meansoperable to form mud flowing through said return conduit means into ajet stream operable to impel pulverulent material discharged by saidfirst vane means; second, relatively high-capacity, mixing means forsupplying pulverulent material to said mixing reservoir means, saidsecond mixing means including second branch conduit means communicatingwith said second discharge conduit means of said solid material supplymeans, said second branch conduit means bypassing said transferreservoir means, valve means, operable in response to saiddensity-measuring means, to control a flow of pressurized air andpulverulent material through said second branch conduit means, outletmeans for discharging pressurized air and pulverulent material from saidsecond branch conduit means toward said mixing reservoir means, secondreturn branch conduit means communicating with said return conduitmeans, annular stream-defining means communicating with said secondreturn branch conduit means and operable to define an annular flow ofmud encircling pressurized air and pulverulent material discharging fromsaid outlet means; additive supplying means including additive materialreservoir means, second vane means operable to define a series ofmutually isolated rotatable pockets for discharging segregatedquantities of additive material from said additive material reservoirmeans, means for selectively controlling the rate of discharge ofadditive material by said vane means, additive material conduit meansfor conveying additive material, discharged by said second vane means,to said mixing reservoir means, and third, return branch conduit meansconnected with said first discharge conduit means, and secondjet-defining means operable to constrain mud flowing through said thirdreturn branch conduit means into a jet stream operable to impel additivematerial through said additive material conduit means; and selectivelyoperable actuating means for alternately actuating said first and secondmixing means.
 6. An apparatus for mixing mud for use in well-drillingoperations, said apparatus comprising: mixing reservoir means; firstdischarge conduit means extending from said mixing reservoir means; pumpmeans operable to convey mud through said first discharge conduit means;density-measuring means connected with said first discharge conduitmeans and operable to measure the density of mud flowing therethrough;said densiTy-measuring means including a source of photons having aphoton energy of between about 0.6 and about 2 Mev. positioned adjacenta vertical flow of said mud, means for collimating the emission ofphotons from said source en route to said mud, shielding means forsubstantially blocking the passage of photons issuing from said mudwhich have a photon energy level of less than about 0.3 Mev. andattenuating the passage of photons issuing from said mud having a photonenergy level of less than about 0.45 Mev. by at least twice the degreeof attenuation of photons issuing from said mud which have a photonenergy level of about 0.6 Mev. or greater, scintillation counting means,means for impinging photons which have been subjected to said blockingand attenuating on said scintillation counting means, and meansmaintaining a lower discrimination level of said scintillation countingmeans at least as low as about 0.05 Mev.; return conduit means includedin said first discharge conduit means and operable to return a portionof mud flow, downstream of said density-measuring means, from said firstdischarge conduit means to said mixing reservoir means; solid materialsupply means including air pressure containing, and enclosure-definingwall means operable to support a mass of pulverulent material, means forsupplying pressurized air to the interior of said enclosure-definingwall means, with said wall means being operable to maintain superambientpressure within said wall means, and second, discharge conduit meansoperable to discharge pressurized air and pulverulent material from saidsupply means; said solid material supply means further including a firstsource of pulverulent, barite-containing material, a second source ofpulverulent, additive material, and means for selectively blendingmaterials from said first and second sources for passage through saidsecond discharge conduit means; first, relatively low-capacity, mixingmeans for supplying pulverulent material to said mixing reservoir means,said first mixing means including transfer reservoir means, first branchconduit means for conveying pressurized air and pulverulent materialfrom said second discharge conduit means of said solid material supplymeans into said transfer reservoir means, first vane means defining aseries of mutually isolated rotatable pockets for dischargingpulverulent material from said transfer reservoir means to said mixingreservoir means, said first vane means defining a seal between theinterior of said transfer reservoir means and said mixing reservoirmeans, first means responsive to said density-measuring means forcontrolling the rate of discharge of pulverulent material from saidtransfer reservoir means by said first vane means, control means forcontrolling said conveying of pressurized air and pulverulent materialthrough said first branch conduit means to said transfer reservoir meansso as to regulate the amount of pulverulent material in said transferreservoir means, first return branch conduit means communicating withsaid return conduit means, comingling means for comingling pulverulentmaterial discharged by said first vane means and mud passing throughsaid first return branch conduit means, said comingling means includingfirst jet-defining means operable to form mud flowing through saidreturn conduit means into a jet stream operable to impel pulverulentmaterial discharged by said first vane means; second relativelyhigh-capacity, mixing means for supplying pulverulent material to saidmixing reservoir means, said second mixing means including second branchconduit means communicating with said second discharge conduit means ofsaid solid material supply means, said second branch conduit meansbypassing said transfer reservoir means, valve means, operable inresponse to said density-measuring mEans, to control a flow ofpressurized air and pulverulent material through said second branchconduit means, said valve means including weir means extending partiallytransversely across said second discharge conduit means, diaphragm meansoperable to move transversely through the interior of said seconddischarge conduit means, generally toward and away from said weir means,and diaphragm moving means operable in response to saiddensity-measuring means, outlet means for discharging pressurized airand pulverulent material from said second branch conduit means towardsaid mixing reservoir means, second return branch conduit meanscommunicating with said return conduit means, annular stream-definingmeans communicating with said second return branch conduit means andoperable to define an annular flow of mud encircling pressurized air andpulverulent material discharging from said outlet means;additive-supplying means including additive material reservoir means,second vane means operable to define a series of mutually isolatedrotatable pockets for discharging segregated quantities of additivematerial from said additive material reservoir means, means forselectively controlling the rate of discharge of additive material bysaid vane means, additive material conduit means for conveying additivematerial discharged by said second vane means to said mixing reservoirmeans, and third, return branch conduit means connected with said firstdischarge conduit means, and second jet-defining means operable toconstrain mud flowing through said third return branch conduit meansinto a jet stream operable to impel additive material through saidadditive material conduit means; and selectively operable actuatingmeans for alternately actuating said first and second mixing means.
 7. Amethod for mixing material, said method comprising: supplying ahigh-density material from first supply means, at a relatively low rate,to reservoir means; supplying high-density material from second supplymeans to said reservoir means at a relatively high rate; measuring thedensity of mixed material in said reservoir means, said measuring beingeffected with radioactive density-measuring means, having a source ofphotons with a photon energy level of between about 0.6 and about 2Mev.; regulating an alternate flow of material through said first andsecond supply means in response to said measuring, while maintaining asubstantially constant calibration of said radioactive density-measuringmeans.
 8. A method for mixing mud to be used in well-drillingoperations, said method comprising: supplying a pulverulentbarite-containing material from first supply means, at a relatively lowrate, to mud-mixing reservoir means; supplying pulverulent,barite-containing material from second supply means to said mixingreservoir means at a relatively high rate; measuring the density of mudin said mixing reservoir means, said measuring being effected bypositioning a source of photons having a photon energy of between about0.6 and about 2 Mev. adjacent a vertical flow of said mud, substantiallyblocking the passage of photons issuing from said mud which have aphoton energy level of less than about 0.3 Mev., and attenuating thepassage of photons issuing from said mud having a photon energy level ofless than about 0.45 Mev. by at least twice the degree of attenuation ofphotons issuing from said mud which have a photon energy level of about0.6 Mev. or greater, and impinging photons which have been subjected tosaid blocking and attenuating on photon-counting means; and alternatelyregulating the flow of pulverulent material through said first andsecond supply means in response to said measuring.
 9. A method formixing mud to be used in well-drilling operations, said methodcomprising: supplying a puLverulent barite-containing material fromfirst supply means, at a relatively low rate, to mud-mixing reservoirmeans; supplying pulverulent, barite-containing material from secondsupply means to said mixing reservoir means at a relatively high rate;measuring the density of mud in said mixing reservoir means, saidmeasuring being effective by positioning a source of photons having aphoton energy of between about 0.6 and about 2 Mev. adjacent a verticalflow of said mud, collimating the emission of photons from said sourceen route to said mud, substantially blocking the passage of photonsissuing from said mud which have a photon energy level of less thanabout 0.3 Mev., attenuating the passage of photons issuing from said mudhaving a photon energy level of less than about 0.45 Mev. by at leasttwice the degree of attenuation of photons issuing from said mud, whichhave a photon energy level of about 0.6 Mev. or greater, impingingphotons which have been subjected to said blocking and attenuating onscintillation counting means, and maintaining a lower discriminationlevel of said scintillation counting means at least as low as about 0.05Mev.; alternately regulating the flow of pulverulent material throughsaid first and second supply means in response to said measuring; andpneumatically impelling said material through each of said first andsecond supply means.
 10. A method for mixing mud to be used in welldrilling operations, said method comprising: supplying a pulverulentbarite-containing material from first supply means, at a relatively lowrate, to mud-mixing reservoir means; supplying pulverulent,barite-containing material from second supply means to said mixingreservoir means at a relatively high rate; measuring the density of mudin said mixing reservoir means, said measuring means being effected bypositioning a Cs 137 source of photons having a photon energy of about0.661 Mev. adjacent a vertical flow of said mud, collimating theemission of photons from said source en route to said mud, substantiallyblocking the passage of photons issuing from said mud which have aphoton energy level of less than about 0.3 Mev., attenuating the passageof photons issuing from said mud having a photon energy level of lessthan about 0.45 Mev. by at least twice the degree of attenuation ofphotons issuing from said mud, which have a photon energy level of about0.6 Mev. or greater, impinging photons which have been subjected to saidblocking and attenuating on a thallium-activated sodium iodide crystal,and maintaining a lower discrimination level of said scintillationcounting means at least as low as about 0.05 Mev.; regulating analternate flow of pulverulent material through said first and secondsupply means in response to said measuring; pneumatically impelling saidmaterial through each of said first and second supply means; addingadditional mud additive substances to said mixing reservoir means at arate of addition independent of said measuring; and impelling at least aportion of said barite material with a mud jet en route to saidreservoir means.
 11. A method for mixing material, said methodcomprising: supplying a high-density material from first supply means,at a relatively low rate, to reservoir means; supplying high-densitymaterial from second supply means to said reservoir means at arelatively high rate; impelling at least a portion of said high-densitymaterial with a mud jet en route to said reservoir means; measuring thedensity of mixed material in said reservoir means, said measuring beingeffected with density-measuring means; regulating an alternate flow ofmaterial through said first and second supply means in response to saidmeasuring, while maintaining a substantially constant calibration Ofsaid density-measuring means.
 12. A method for mixing material, saidmethod comprising: supplying a high-density material from first supplymeans, at a relatively low rate, to reservoir means; supplyinghigh-density material from second supply means to said reservoir meansat a relatively high rate; pneumatically impelling said high-densitymaterial through each of said first and second supply means; measuringthe density of mixed material in said reservoir means, said measuringbeing effected with measuring means; and regulating an alternate flow ofmaterial through said first and second supply means in response to saidmeasuring, while maintaining a substantially constant calibration ofsaid measuring means.
 13. An apparatus for mixing material, saidapparatus comprising: reservoir means; first supply means for supplyinga high-density material, at a relatively low rate, to said reservoirmeans; second supply means for supplying a high-density material to saidreservoir means at a relatively high rate; means for pneumaticallyconveying said high-density material through each of said first andsecond supply means; and density-measuring means operable to measure thedensity of material mixed in said reservoir means, saiddensity-measuring means being operable, substantially independent of thecomposition of said mixed material, to indicate mixed material density,with the calibration of said measuring means being substantially thesame when each of said first and second supply means is independentlysupplying material to said reservoir means.
 14. An apparatus for mixingmaterial, said apparatus comprising: reservoir means; first supply meansfor supplying a high-density material, at a relatively low rate, to saidreservoir means, said first supply means including a transfer reservoirmeans; second supply means for supplying a high-density material to saidreservoir means at a relatively high rate; and density-measuring meansoperable to measure the density of material mixed in said reservoirmeans, said density-measuring means including density-measuring meansoperable, substantially independent of the composition of said mixedmaterial, to indicate mixed material density, with the calibration ofsaid density-measuring means being substantially the same when each ofsaid first and second supply means is independently supplying materialto said reservoir means.
 15. An apparatus for mixing mud for use inwell-drilling operations, said apparatus comprising: mixing reservoirmeans; first discharge conduit means extending from said mixingreservoir means; pump means operable to convey mud through said firstdischarge conduit means; density-measuring means connected with saidfirst discharge conduit means and operable to measure the density of mudflowing therethrough; return conduit means included in said firstdischarge conduit means and operable to return a portion of mud flow,downstream of said density-measuring means, from said first dischargeconduit means to said mixing reservoir means; solid material supplymeans including air pressure containing, and enclosure-defining wallmeans operable to support a mass of pulverulent material, means forsupplying pressurized air to the interior of said enclosure-definingwall means, with said wall means being operable to maintain superambientpressure within said wall means, and second, discharge conduit meansoperable to discharge pressurized air and pulverulent material from saidsupply means; and mixing means for supplying pulverulent material tosaid mixing reservoir means, said mixing means including transferreservoir means, branch conduit means for conveying pressurized air andpulverulent material from said second discharge conduit means of saidsolid material supply means into said transfer reservoir means,material-transferring seal means defining a seal between the intErior ofsaid transfer reservoir means and said mixing reservoir means, butoperable to discharge pulverulent material to said mixing reservoirmeans, means responsive to said density-measuring means for controllingthe rate of discharge of pulverulent material from said transferreservoir means by said seal means, control means for controlling saidconveying of pressurized air and pulverulent material through saidbranch conduit means to said transfer reservoir means so as to regulatethe amount of pulverulent material in said transfer reservoir means,return branch conduit means communicating with said return conduitmeans, and comingling means for comingling pulverulent materialdischarged by said seal means and mud passing through said return branchconduit means, said comingling means including jet-defining meansoperable to form mud flowing through said return conduit means into ajet stream operable to impel pulverulent material discharged by saidseal means.
 16. An apparatus for mixing mud for use in well-drillingoperations, said apparatus comprising: mixing reservoir means; firstdischarge conduit means extending from said mixing reservoir means; pumpmeans operable to convey mud through said first discharge conduit means;density-measuring means connected with said first discharge conduitmeans and operable to measure the density of mud flowing therethrough;said density-measuring means including a source of photons having aphoton energy of between about 0.6 and about 2 Mev. positioned adjacenta vertical flow of said mud, means for collimating the emission ofphotons from said source en route to said mud, shielding means forsubstantially blocking the passage of photons issuing from said mudwhich have a photon energy level of less than abut 0.3 Mev. andattenuating the passage of photons issuing from said mud having a photonenergy level of less than about 0.45 Mev. by at least twice the degreeof attenuation of photons issuing from said mud which have a photonenergy level of about 0.6 Mev. or greater, scintillation counting means,means for impinging photons which have been subjected to said blockingand attenuating on said scintillation counting means, and meansmaintaining a lower discrimination level of said scintillation countingmeans at least as low as about 0.05 Mev.; return conduit means includedin said first discharge conduit means and operable to return a portionof mud flow, downstream of said density-measuring means, from said firstdischarge conduit means to said mixing reservoir means; solid materialsupply means including air pressure containing, and enclosure-definingwall means operable to support a mass of pulverulent material, means forsupplying pressurized air to the interior of said enclosure-definingwall means, with said wall means being operable to maintain superambientpressure within said wall means, and second, discharge conduit meansoperable to discharge pressurized air and pulverulent material from saidsupply means; said solid material supply means further including a firstsource of pulverulent, barite-containing material, a second source ofpulverulent, additive material, and means for selectively blendingmaterials from said first and second sources for passage through saidsecond discharge conduit means; and mixing means for supplyingpulverulent material to said mixing reservoir means, said mixing meansincluding transfer reservoir means, branch conduit means for conveyingpressurized air and pulverulent material from said second dischargeconduit means of said solid material supply means into said transferreservoir means, vane means defining a series of mutually isolatedrotatable pockets for discharging pulverulent material from saidtransfer reservoir means to said mixing reservoir means, said vane meansdefining a seal Between the interior of said transfer reservoir meansand said mixing reservoir means, means responsive to saiddensity-measuring means for controlling the rate of discharge ofpulverulent material from said transfer reservoir means by said vanemeans, control means for controlling said conveying of pressurized airand pulverulent material through said branch conduit means to saidtransfer reservoir means so as to regulate the amount of pulverulentmaterial in said transfer reservoir means, return branch conduit meanscommunicating with said return conduit means, and comingling means forcomingling pulverulent material discharged by said vane means and mudpassing through said return branch conduit means, said comingling meansincluding jet-defining means operable to form mud flowing through saidreturn conduit means into a jet stream operable to impel pulverulentmaterial discharged by said vane means.
 17. An apparatus for mixing mudfor use in well-drilling operations, said apparatus comprising: mixingreservoir means; first discharge conduit means extending from saidmixing reservoir means; pump means operable to convey mud through saidfirst discharge conduit means; density-measuring means connected withsaid first discharge conduit means and operable to measure the densityof mud flowing therethrough; return conduit means included in said firstdischarge conduit means and operable to return a portion of mud flow,downstream of said density-measuring means, from said first dischargeconduit means to said mixing reservoir means; solid material supplymeans including air pressure containing, and enclosure-defining wallmeans operable to support a mass of pulverulent material, means forsupplying pressurized air to the interior of said enclosure-definingwall means, with said wall means being operable to maintain superambientpressure within said wall means, and second, discharge conduit meansoperable to discharge pressurized air and pulverulent material from saidsupply means; and mixing means for supplying pulverulent material tosaid mixing reservoir means, said mixing means including branch conduitmeans communicating with said second discharge conduit means of saidsolid material supply means, said branch conduit means bypassing saidtransfer reservoir means, valve means, operable in response to saiddensity-measuring means, to control a flow of pressurized air andpulverulent material through said branch conduit means, outlet means fordischarging pressurized air and pulverulent material from said branchconduit means toward said mixing reservoir means, return branch conduitmeans communicating with said return conduit means, and annularstream-defining means communicating with said return branch conduitmeans and operable to define an annular flow of mud encirclingpressurized air and pulverulent material discharging from said outletmeans.
 18. An apparatus for mixing mud for use in well-drillingoperations, said apparatus comprising: mixing reservoir means; firstdischarge conduit means extending from said mixing reservoir means; pumpmeans operable to convey mud through said first discharge conduit means;density-measuring means connected with said first discharge conduitmeans and operable to measure the density of mud flowing therethrough;said density-measuring means including a source of photons having aphoton energy of between about 0.6 and about 2 Mev. positioned adjacenta vertical flow of said mud, means for collimating the emission ofphotons from said source en route to said mud, shielding means forsubstantially blocking the passage of photons issuing from said mudwhich have a photon energy level of less than about 0.3 Mev. andattenuating the passage of photons issuing from said mud having a photonenergy level of less than about 0.45 Mev. by at least twice the degreeof attenuation of photons issuing from said mud which have a photonenergy level of about 0.6 Mev. or greater, scintillation counting means,means for impinging photons which have been subjected to said blockingand attenuating on said scintillation counting means, and meansmaintaining a lower discrimination level of said scintillation countingmeans at least as low as about 0.05 Mev.; return conduit means includedin said first discharge conduit means and operable to return a portionof mud flow, downstream of said density-measuring means, from said firstdischarge conduit means to said mixing reservoir means; solid materialsupply means including air pressure containing, and enclosure-definingwall means operable to support a mass of pulverulent material, means forsupplying pressurized air to the interior of said enclosure-definingwall means, with said wall means being operable to maintain superambientpressure within said wall means, and second, discharge conduit meansoperable to discharge pressurized air and pulverulent material from saidsupply means; said solid material supply means further including a firstsource of pulverulent, barite-containing material, a second source ofpulverulent, additive material, and means for selectively blendingmaterials from said first and second sources for passage through saidsecond discharge conduit means; and mixing means for supplyingpulverulent material to said mixing reservoir means, said mixing meansincluding branch conduit means communicating with said second dischargeconduit means of said solid material supply means, said branch conduitmeans bypassing said transfer reservoir means, valve means, operable inresponse to said density-measuring means, to control a flow ofpressurized air and pulverulent material through said branch conduitmeans, said valve means including weir means extending partiallytransversely across said second discharge conduit means, diaphragm meansoperable to move transversely through the interior of said seconddischarge conduit means, generally toward and away from said weir means,and diaphragm moving means operable in response to saiddensity-measuring means, outlet means for discharging pressurized airand pulverulent material from said branch conduit means toward saidmixing reservoir means, return branch conduit means communicating withsaid return conduit means, and annular stream-defining meanscommunicating with said return branch conduit means and operable todefine an annular flow of mud encircling pressurized air and pulverulentmaterial discharging from said outlet means.
 19. An apparatus for mixingmaterial, said apparatus comprising: reservoir means; pneumatic meansfor conveying pneumatically impelled material toward said reservoirmeans; means operable to flow with said pneumatically conveyed materialtoward said reservoir means; means to comingle at least a portion ofsaid material with a mud jet en route to said reservoir means; anddensity-measuring means operable to measure the density of materialmixed in said reservoir means, said density-measuring means includingradioactive density-measuring means operable, substantially independentof the composition of said mixed material, to indicate mixed materialdensity.
 20. Apparatus for mixing material, said apparatus comprising:means for supplying pulverulent material from supply means to mixingreservoir means; means for measuring the density of mixed material insaid mixing reservoir means, said measuring means including meanspositioning a source of photons having a photon energy of between about0.6 and 2 Mev. adjacent a flow of said mixed material, meanssubstantially blocking the passage of photons issuing from said mixedmaterial which have a photon energy level of less than about 0.3 Mev.,means attenuating the passage of photons issuing from said mixedmaterial having a photon energy level of less than about 0.45 Mev. by atleast twice the degree of attenuation of photons issuing from said mixedmaterial which have a photon energy level of about 0.6 Mev. or greater,and means for impinging photons which have been subjected to saidblocking and attenuating on photon counting means; means regulating aflow of pulverulent material through said supply means in response tosaid measuring; means pneumatically impelling said pulverulent materialthrough said supply means; and means conveying at least a portion ofsaid pulverulent material with liquid en route to said reservoir means.21. A method for mixing material, said method comprising: pneumaticallyimpelling material toward reservoir means; conveying said pneumaticallyimpelled material with a liquid stream toward said reservoir means;measuring the density of material mixed in said reservoir means withdensity-measuring means including radioactive density-measuring meansoperable, substantially independent of the composition of said mixedmaterial, to indicate mixed material density; and regulating the flow ofsaid pneumatically impelled material in response to said measuring. 22.A method for mixing material, said method comprising: supplyingpulverulent material from supply means to mixing reservoir means;measuring the density of mixed material in said mixing reservoir means,said measuring means being effected by positioning a source of photonshaving a photon energy of between about 0.6 and 2 Mev. adjacent a flowof said mixed material, substantially blocking the passage of photonsissuing from said mixed material which have a photon energy level ofless than about 0.3 Mev., attenuating the passage of photons issuingfrom said mixed material having a photon energy level of less than about0.45 Mev. by at least twice the degree of attenuation of photons issuingfrom said mixed material, which have a photon energy level of about 0.6Mev. or greater, and impinging photons which have been subjected to saidblocking and attenuating on photon counting means; regulating a flow ofpulverulent material through said supply means in response to saidmeasuring; pneumatically impelling said pulverulent material throughsaid supply means; and conveying at least a portion of said pulverulentmaterial with a liquid en route to said reservoir means.